The major histocompatibility antigens are comprised of two chains--H2 (45,000 MW) and beta-2 microglobulin (12,000 MW). A major goal of my laboratory is to understand the organization and regulated expression of the genes that encode these antigens. The regulation of the expression of these genes is of interest for two reasons. 1) These genes are examples of 'housekeeping' genes (i.e. genes that are expressed in every cell at a low level). I believe that comparison of the sequences involved in the regulation of expression of these genes with the sequences involved in the regulation of genes expressed at high levels in particular cells may reveal useful information about mechanisms of differentiation. 2) Since the histocompatibility antigens seem to play a role in various cellular interactions the mechanisms that determine their expression may eventually lead to a better understanding of these cellular events. We hope to use recombinant DNA technologies to study the organization and expression of these genes. During the past year we have begun to study the organization of the mouse beta-2 microglobulin gene. We began by cloning a beta-2 microglobulin cDNA. Using this cloned cDNA sequence we have: 1) isolated a bacteriophage clone that encodes the mouse beta-2 microglobulin gene, 2) shown that a particular cell that was selected as a TL deficient cell line is actually a beta-2 microglobulin deficient cell line. We propose to: 1) complete the characterization of the structural gene for beta-2 microglobulin, 2) isolate mutations in the beta-2 microglobulin gene and 3) characterize the effects of these mutations in in vitro transcription assays in in vivo. The beta-2 microglobulin gene is well suited for these studies because the gene is relatively small (less then 3000 bp), the polypeptide is only 100 aminoacids long, the protein product can be detected in small amounts, there is a selection for cells lacking beta-2 microglobulin and there is at least one cell that has lost its beta-2 microglobulin gene. Thus, we believe that a mutational analysis of the beta-2 microglobulin gene is feasible and should lead to a better understanding of the sequences involved in regulating the expression of this gene.